1. Technical Field
The present invention relates to wafer transfer, and more particularly to methods for transferring layers or substrates by controlling crack propagation.
2. Description of the Related Art
Wafer transfer processing is employed to transfer layers from one substrate to another. There is interest in processes that can separate a device layer from an underlying single crystal base substrate while leaving the base substrate smooth enough to not require a significant amount of polishing before the substrate is used again. In one process, an epitaxial lift-off procedure utilizes an AlAs separation layer between a base substrate (e.g., Ge or GaAs) and a III-V epitaxial device layer and separates the epitaxial layer from the base substrate layer by laterally etching the AlAs layer with HF. This approach is very time-consuming to the point that it is not practical for manufacturing, especially for large area wafers.
In another process, spalling is employed. In this approach, a metallic stress layer is deposited on a layer stack that includes a substrate, epitaxial buffer layer and a III-V device layer. The structure is then cracked by splitting the buffer layer, followed by a selective etch to remove buffer layer residuals from either side of the crack face. However, the depth of the crack can be difficult to control and it cannot always be confined to the buffer layer.